1. Field of the Invention
The present invention relates to an ink jet apparatus that prints by ejecting ink from ejection openings of an ink jet head and causing the ink to adhere to a material on which printing is to be effected (hereinafter referred to as "print material"). In particular, the present invention relates to an ink jet apparatus that is equipped with a wiping device that wipes that surface of the ink jet head on which the ejection openings are formed (hereinafter referred to as the "ejection surface") in order to enable the ink jet head to maintain a stable ink ejecting function.
2. Description of the Related Art
A printing apparatus having the function of a printer, copying machine, facsimile apparatus or the like, or a printing apparatus used as the output apparatus of a composite-type electronic apparatus including a computer, word processor and the like, or a printing apparatus used as the output apparatus of a work station, is designed such that images are successively printed on a print material consisting of a printing medium, such as paper or a thin plastic plate. Depending on the printing method, such printing apparatuses can be classified into ink jet type apparatuses, wire dot type apparatuses, thermal type apparatuses, laser beam type apparatuses, etc.
In a serial-type printing apparatus, a serial scanning system is employed, in which the main scanning is performed in a direction that crosses the print material conveying direction, which is the sub-scanning direction for the print material. In this serial-type printing apparatus, the print material is set at a predetermined printing position, and then an image portion corresponding to one line is printed on the print material through the main scanning by a printing device mounted on a carriage that is movable along the print material. After the completion of the printing of the above image portion, corresponding to one line, a paper feeding process called "pitch feed" is performed to feed the print material by a predetermined amount. After this, the printing of an image portion corresponding to the next line is performed on the print material, which is at rest. By repeating this series of operations, printing is effected on the entire print material. In a line-type printing apparatus, which prints solely by sub-scanning, performed in the print material feeding direction, the print material is set at a predetermined printing position, and the printing of an image portion corresponding to one line is collectively effected. After this, the print material is fed by a predetermined amount, and then the printing of an image portion corresponding to the next line is collectively effected. By repeating these operations, printing is performed on the entire print material.
Of the printing apparatuses mentioned above, the ink jet printing apparatus employing an ink jet system in which ink is ejected from the printing device to the print material provides various advantages. For example, the ink jet printing apparatus can be easily built in a small size. Further, with the ink jet printing apparatus, it is possible to print a high-resolution image at high speed. The ink jet printing apparatus allows printing on an ordinary paper without requiring any special processing for the paper, and requires a low running cost. Further, due to its non-impact system, it is relatively free from noises. In addition, it enables a color image to be easily printed by using inks of different colors. In particular, when the ink jet printing apparatus is a line type printing apparatus that uses a line type printing device in which a multitude of ejection openings are arranged along the paper direction, a further increase in printing speed is possible.
In particular, an ink jet printing apparatus of a type which ejects ink by utilizing heat energy can be easily produced as a printing apparatus exhibiting a high-density liquid passage arrangement. Such a high-density liquid passage arrangement can be realized by forming electro-thermal converters, electrodes, liquid passage walls, top plates, etc. through film formation on a substrate by using a semiconductor manufacturing process, such as etching, evaporation, or sputtering. This arrangement allows a further reduction in size. Regarding the print material, various requirements should be taken into consideration. Apart from the ordinary print materials, such as paper and thin plastic plates (OHP or the like), use of thin paper or processed paper (e.g., paper with punch holes or perforation for filing or paper with an arbitrary configuration) has recently come to be required.
FIG. 8 is a schematic diagram illustrating the positional relationship between the ink jet head, carriage and cleaning blade in a conventional ink jet apparatus.
In FIG. 8, numeral 1 indicates an ink jet head that is integrally combined with an ink tank to form an ink jet cartridge. The ink jet head 1 is carried by a carriage 2 that is slidably mounted on a guide rail 3. The ink jet head 1 is equipped with a plurality of ejection openings, and ejects ink from the plurality of ejection openings as it reciprocates with the carriage 2 in the main scanning directions indicated by the arrows S, thereby performing printing. The carriage 2 further carries a carriage spur (not shown), which is mounted on the carriage 2 at a position in the vicinity of the ink jet head 1. The carriage spur is rotatably mounted such that, when brought into contact with the print material, the carriage spur is displaced while rolling on the print material as the carriage 2 reciprocates. Due to this arrangement, the minimum requisite gap is ensured between the print material and the ink jet head 1 even when the print material is deflected to exhibit a local swell. In this way, the print material is kept from coming into contact with the ink jet head 1.
A cleaning blade 18 cleans the ejection surface of the ink jet head 1. The cleaning blade 18 is formed as a one-piece plate of urethane rubber, HNBR or the like and has a thickness of, for example, 0.5 mm. When cleaning is performed, the cleaning blade 18 is positioned such that it overlaps the ejection surface of the ink jet head 1 to wipe away paper powder, dust, residuary ink and the like adhering to the ejection surface when the ink jet head 1, mounted on the carriage 2, passes the cleaning blade 18. During the preparation of the ink jet head 1, its ejection surface is subjected to surface treatment such that the ejection surface exhibits a uniform ink wettability.
Due to the fact that the ejection surface is wiped with a one-piece cleaning blade, the above-described conventional ink jet apparatus cannot sufficiently cope with such problems as unevenness in the ink wettability of the ejection surface or unevenness in the pressure distribution of the cleaning blade, resulting in some residuary ink being allowed to remain unwiped. This problem is particularly conspicuous when the ejection surface has some surface irregularities or when the ink jet apparatus is a color type ink jet apparatus in which the nozzle of an ink jet head is divided into several parts that are respectively supplied with inks of different colors.
Japanese Patent Laid-Open No. 62-101448 discloses a construction in which the blade forward-end portion is separated into a plurality of parts and in which the divisional widths are varied in accordance with the head configuration. However, even with this construction, it is not always possible to solve the above problem. In the above-mentioned color-type ink jet head, in particular, in which the ink composition differs from color to color, the problem of some residuary ink being allowed to remain unwiped and the problem of the surface-treated ejection surface being worn are conspicuous. Further, defective ink ejection is also to be observed. Furthermore, there is a problem of color mixing, i.e., mixing of inks of different colors in the nozzle section. Under the circumstances, there is a demand for an improvement in printing quality.